Effects of interferon and PKC modulators on human glioma protein kinase C, cell proliferation, and cell cycle.

The in-vitro effects of human interferon alpha-2b (HuIFN alpha-2b), protein kinase C (PKC) agonist [TPA (12-0-tetra-decanoyl-phorbol-13-acetate)] and PKC inhibitor (calphostin C) on human glioma (U-373 MG) PKC activity, cell proliferation and cell cycle were compared. HuIFN alpha-2b and TPA increased PKC activity, elevated the number of cells in DNA synthesis (S) phase and decreased cell proliferation by similar magnitudes. Calphostin C inhibited PKC activity, increased the number of cells in S phase and produced strong cytotoxic effects (IC50 150 nM). Higher concentrations of calphostin C with or without serum induced an additional block in gap2 and mitosis. We conclude that HuIFN alpha-2b's mode of action may be directly or indirectly affecting PKC. The response produced by HuIFN alpha-2b is similar to TPA (potent PKC activation and S phase arrest).